Molding apparatus for grinding wheels



June 9, 1964 D. A. CALDERWOOD ETAL 3,135,999

MOLDING APPARATUS FOR GRINDING WHEELS Filed Nov. 25. 1960 INVENTORS DON D A. CALDERWOOD JOH SZLACHETKA @225 BY AQ fl/Qk ATTORNEY United States Patent O 3,135,999 MOLDING APPARATUS FOR GRINDING WHEELS Donald A. Calderwood, Pittsburgh, and John A. Szlachetlra, Cheswick, Pa., assignors to Armstrong & White, Cheswick, Pa., a corporation of Pennsylvania Filed Nov. 23, 1960, Ser. No. 71,246 7 Claims. (Cl. 18-36) This invention relates to improved molding apparatus for the manufacture of abrasive grinding wheels and the like.

More specifically, the present invention is related to a pin-and-sleeve assembly for securing a threaded hub structure within molding apparatus to assure the production of abrasive grinding wheels having such threaded hubs concentrically positioned and having their geometric axis maintained normal to the rotating plane of such abrasive grinding wheels.

In the usual manufacture of abrasive grinding wheels, metal mold structures are provided with a bottom element and a correlative upper element which are brought together to define a molding cavity having the configuration of the desired abrasive grinding wheel. Suitable pulverulent abrasive wheel forming compositions are poured into the cavity to form the grinding wheel. Such compositions might include, for example, abrasive solid particles (sand, carborundum, diamond chips and similar hard materials) combined with suitable thermosetting resinous plastic compositions such as phenolic resins. Such compositions might be of vitreous character. The exact composition forms no part of the present invention, it being understood that the present invention is concerned with the molding apparatus which can be employed with any of these compositions.

Upon the application of heat, or other suitable composition-solidifying conditions, the pulverulent composition is solidified within the cavity into a solid structure which is thereafter removed from the molding apparatus and used as an abrasive grinding Wheel.

It is customary in the grinding wheel industry to supply such abrasive grinding wheels with metal inserts having a threaded hub portion whereby the wheels may be aifixed to rotatable shafts for use. The threaded hubs permit rapid and simple installation and replacement of such grinding wheels. Usually the hub portion has a plurality of radially extended ears which are disposed within the mold cavity and are engulfed and surrounded by the molding wheel forming composition during the mold filling operation. ;The completed solidified Wheel, thus, has the hub portion securely retained at its center.

However, the industry has found difliculties (1) in maintaining the hub portions at the exact center of the mold cavity and also has found difficulties (2) in maintaining the hub structure with the axis of the threaded hub normal to the plane of the abrasive wheel. Where the hub portion is not concentric, the resulting wheel, when mounted upon a shaft, will rotate eccentrically and will be of little value until the eccentricity has been eliminated through Wear. Where the axis of the hub structure is not normal to the plane of the abrasive grinding wheel, the resulting wheel, when mounted upon a shaft, will wobble and will never be of value. Such abrasive grinding wheels must be discarded.

The principal object of the present invention is to provide a mold assembly for the manufacture of abrasive grinding wheels having means for securing the hub portion of such wheels in a concentric location with respect to the mold cavity and further for securing the hub portion so that the axis of the threaded hub will be maintained normal to the plane of the resulting wheel.

A further object of this invention is to provide the described mold assembly which can be directly applied to molding apparatus of the conventional type currently found in industry.

A still further object of this invention is to provide a mold assembly which can be adapted to secure hub structures regardless of the normal dimensional tolerances encountered in the threaded hubs.

Another object of this invention is to provide a hubcentering structure which may be utilized in the assembly of metal hub structures in preformed abrasive grinding Wheels, particularly vitreous wheels.

These and other objects and advantages of the present invention will become apparent from the following detailed description in reference to the accompanying drawings in which:

FIGURE 1 is a cross-section illustration of a conventional two-piece molding apparatus for forming abrasive grinding wheels;

FIGURE 2 is a cross-section illustration of a two-piece molding apparatus for forming abrasive wheels according to the present invention;

FIGURE 3 is a perspective illustration of a hub-holding sleeve according to a preferred embodiment of the present invention; and

FIGURE 4 is a perspective illustration of a sleeveengaging pin according to a preferred embodiment of the present invention along with a pin holder.

Referring to FIGURE 1, there is illustrated a conventional two-piece molding apparatus as employed in the industry at the present time. The apparatus includes a bottom element 10 and an upper element 11 which are correlated so that, when brought together in mating relation, a mold cavity 12 is formed which has the configuration desired in the resultant abrasive grinding wheel. Both the bottom element 10 and the upper element formed from metals, usually steel.

Concentrically within the bottom mold element 10 is a first bore 13 which receives a pin 14 having an outer diameter in its lower portion only slightly less than the inner diameter of the bore 13. The diiference in diameters may be from about 0.001 to about 0.005 inch. The upper portion of the pin 14 has a greater diameter which is slightly less than the minimum diameter of the threaded hubs normally encountered in production. The largerdia'meter upper portion of the pin 14- terminates in a shoulder 15 at the center of the pin 14 where the smaller diameter lower portion commences. This shoulder 15 rests upon the upper surface 16 of the bottom mold element 1%).

The internally threaded hub structure is identified by the numeral 17. The structure comprises usually a flat disk 18 having radially extended bent ears 19 which are extended within the mold cavity 12 and which are engulfed and surrounded by the abrasive wheel forming composition which is subsequently poured into the mold cavity 12.

Secured at the center of the fiat disk 18 is a tubular hub 20 usually having a roughened outer surface and a threaded bore 21. In the manufacture of the threaded bore 21, there is an appreciable variation in the inner diameter which is observed in most threading operations. The actual inner diameter of the threaded bore 21 may vary 0.010 inch or more from the desired dimension. The pin 14 has its upper portion of such diameter that the minimum diameter of the threaded bore 21 may be readilyaccommodated. Thus, when hub structures 17 having greater than the minimum diameter bore are provided-and there is substantial variation in the inner diameter of the threaded bores 21 from one hub structure to the next onethere is a resulting loose engagement between the threaded bore 21 and the pin 14. The

looseness permits the hub structure to move into positions where it is not concentric with the mold cavity 12. The

resulting abrasive grinding wheels possess eccentricity.

Normally the hub structure 17 rests upon the upper surface 16 of the bottom mold element 10, and, when this is so, the geometric axis of the threaded bore 21 is normal to the rotation plane of the resulting grinding wheel. However, through continued use, some wear results in the lower portion of the pin 14 and the bore 13 so that the pin 14 may not necessarily fit tightly and vertically. In such cases, it is frequently found that the geometric axis of the threaded bore 21 is not normal with the rotation plane of the resulting grinding wheel. Wobbling wheels are produced in such instances which are useless.

Further continuing the description of the present molding operations, it will be observed that the upper mold element 11 has a bore 22 in which a metal cylinder 23 is slidable. The metal cylinder 23 has a diameter corresponding to the outer diameter of the hub 20. The function of the metal cylinder 23 is to cover the exposed end portion of the hub 29 to prevent entry of any abrasive wheel forming composition into the threaded bore 21. The upper mold element 11 is slipped downwardly over the metal cylinder 23 when the mold is assembled for use. Occasionally a recess 24 is provided in the metal cylinder 23 to receive the pin 14. When the recess 24 is provided, a bore 25 may be provided to facilitate removal of the pin 14 from the metal cylinder 23 when replacement of the pin 14 of the metal cylinder 23 is required.

According to the present invention, concentricity of the Wheel hub structure is assured; maintenance of the geometric axis of the threaded bore of the hub structure normal to the rotating plane of the abrasive grinding wheel is assured.

This is accomplished by providing a radially slotted sleeve element and a mating radially slotted pin element to replace the usual pin member 14 described in relation to FIGURE 1. The slotted sleeve has a normal outer diameter corresponding to the normal inner diameter encountered in threaded hubs. The slotted pin has a normal outer diameter slightly greater than the normal inner diameter of the slotted sleeve. Both the slotted sleeve and the slotted pin are expansible and contractible in their diameters whereby variations in the diameters of threaded hubs from one to another can be accommodated.

Specifically, referring to FIGURE 2, the bottom mold element 10 and the upper mold element 11 are unchanged from their conventional appearance. Corresponding numerals are employed in FIGURE 2 to identify corresponding elements already described in reference to FIGURE 1.

A sleeve 30, engaged in the bore 13 of the bottom mold element 10, is more clearly illustrated in FIGURE 3 wherein the upper portion 31 has a greater normal outer diameter than the lower portion 32. At the central portion of the sleeve 30, the upper portion 31 and the lower portion 32 are separated by a shoulder 33 which normally rests upon the upper surface 16 of the bottom mold element 10. The inner bore 34 of the sleeve has a constant normal diameter. It will be observed that the sleeve 30 has a plurality of longitudinal slots 35 extending through the lower portion 32 into the upper portion 31. Further longitudinal slots 36 are provided through the upper portion 31 into the lower portion 32. The longitudinal slots 35, 36 alternate over the periphery of the sleeve 30 which, in effect, becomes a slotted collet sleeve.

By virtue of the slotted collet sleeve construction, the lower portion 32 of the sleeve 30 can be contracted in its diameter to provide a tight fit in the bore 13. The normal outer diameter of the lower portion 32 is slightly greater than the inner diameter of the bore 13 to assure 4 the tight fit. The bottom terminus of the sleeve 30 is tapered to facilitate introduction of the lower portion 32 into the bore 13.

The upper portion 31 of the sleeve 30 has a normal diameter which corresponds to the normal diameter of threaded hubs encountered in production. Thus the hub 17 can be easily fitted over the upper portion 31 of the sleeve 30 within the mold cavity 12. The upper edge of the sleeve 30 is tapered to facilitate the slippage of the hub 17 over the upper portion 32.

Thus hubs 17 of minimum diameter in their threaded bores 21 are securely maintained concentrically Within the mold cavity 12 by virtue of contraction of the sleeve 30. Hubs 17 having larger than normal bore diameters are initially free to move somewhat within the mold cavity 12.

To accommodate these larger hubs 17, a split pin 37 is provided, more clearly illustrated in FIGURE 4. It will be observed that the pin 37 had an unslotted portion 38 and a slotted portion 39. The unslotted portion 38 is press-fitted into a recess 24 within the pin holder 23 (corresponding to the metal cylinder 23 of FIGURE 1).

The unslotted portion 39 extends outwardly from the pin holder 23 and has a plurality of radial slots 40. A peripheral groove 41 is provided in the inboard terminus of the slotted portion 39 to provide suitable resiliency for the elements of the slotted portion and further to permit the elements of the slotted portion 39 to contract generally radially rather than conically. An axial bore 43 is provided through the slotted portion 39 of the pin 37 to provide additional resiliency of the pin 37.

The slotted portion 39 of the pin 37 has a normal outer diameter slightly greater than the normal inner diameter of the bore of the sleeve 30. The outer edges of the slotted end portion 39 are tapered to facilitate introduction of the pin 37 into the bore of the sleeve 39. The slotted portion 39 of the pin 37 resiliently urges the upper portion 31 of the sleeve 30 radially outwardly until it is in peripheral engagement with the threaded bore 21 of the hub 17. Thus the slotted portion 31 of the sleeve 30 expands to engage those threaded bores 21 having larger than normal diameters under the resilient urging of the slotted portion 39 of the pin 37. Where threaded bores 21 are of the minimum diameter, obviously the upper portion 31 of the sleeve 30 cannot expand outwardly. In these situations, the slotted portion 39 of the pin 37 readily resiliently contracts to maintain a tight engagement of the meshing elements.

The pin holder 23 has a fiat end surface 42 which corresponds to the flat end surface of the hub 17 to prevent entry of abrasive Wheel forming compositions into the threaded bore 21 of the hub 17 during molding operations.

When the abrasive grinding wheel has solidified, the mold structure is dismantled by separating the upper element 11 from the bottom element 10. The pin holder 23 remains with the resulting grinding wheel and is merely lifted from the hub 20 after the upper mold element 11 has been removed. The pin 30, press-fitted in the pin holder 23, is removed by lifting the pin holder 23 away from the hub 20. The abrasive wheel which engulfs and surrounds the hub structure 17 is thereafter removed from the bottom mold element 10 along with the sleeve 30. The sleeve 30 is slipped out from the threaded bore 21 and is available for re-use. Mold release pins (not shown) frequently are provided in the bottom mold element 10 to facilitate removal of the product grinding wheel from the bottom mold element 10. Mold release pins, for example, might slide vertically upwardly through various bores in the bottom mold element 10 such as the bore 13.

Frequently the bottom element 10 of the mold is fabricated in two pieces which can be separated after formation of the abrasive grinding wheel to facilitate its removal from the mold elements.

The present structure also may be utilized as hubin preformed grinding wheels. Vitreous grinding wheels, for example, are fabricated in the desired shapes and baked at high temperatures in order to fuse the vitreous components. The temperatures which are employed would adversely affect any preliminarily installed metal hub element. Hence, the formed vitreous grinding wheels are fitted with metal hubs by means of suitable adhesives. The problems of mass concentricity and geometric axis normality (with the plane of rotation) of the hub element is substantially the same as that described in the foregoing discussion of wheel molding operations.

By means of the present invention, the preformed abrasive wheel may be centered peripherally in a base (such as the bottom mold element and the necessary metal hub may be accurately centered and positioned by means of the pin 37 and sleeve 30 assembly until applied adhesives have set.

We claim:

1. A centering structure for a hub of an abrasive wheel including:

a bottom element peripherally supporting and defining an abrasive wheel composition;

a correlative upper element cooperating with said bottom element;

a first bore in the center of said bottom element and a second bore in the center of said upper element;

a sleeve having longitudinal radial slots and having a first normal diameter extending from a first end thereof to a central portion corresponding with the inner diameter of said first bore and having a second and larger constant normal diameter extending from said central portion to the other end thereof, the said central portion comprising a peripheral shoulder on said sleeve;

a pin radially slotted at one end and having a normal outer diameter slightly greater than the normal inner diameter of said sleeve;

a pin holder comprising a cylinder having a bore in which the unslotted portion of said pin is engaged;

said pin holder being engageable within said second bore of said upper element and having a bottom surface engageable with the said hub over its normally exposed surface;

said pin having its slotted portion engaged within the said sleeve, whereby said sleeve is resiliently engaged over its outer surface with the hub bore and engaged over its inner surface with the said pin to hold said hub rigidly in place upon said bottom element.

2. In a mold for an abrasive wheel having an insert hub structure, said mold having a bottom element and a correlative upper element, an improved holding structure for said insert hub comprising a first bore in the center of said bottom element and a second bore in the center of said upper element,

a sleeve having longitudinal radial slots and having a first constant normal outer diameter extending from a first end thereof to a central portion thereof cor responding with the inner diameter of said first bore and having a second and larger constant normal diameter extending from said central portion to the other end thereof, the said central portion comprising a peripheral shoulder on said sleeve,

a pin radially slotted at one end and having a normal outer diameter slightly greater than the normal inner diameter of said sleeve,

a pin holder comprising a cylinder having a bore in which the unslotted portion of said pin is engaged,

said pin holder being engageable within said second bore of said upper element and having a bottom surface engageable with the said hub over its normally exposed surface,

said pin having its'slotted portion engaged within the said sleeve, whereby said sleeve is resiliently engaged over its outer surface with the hub bore and engaged over its inner surface with the said pin to hold said hub rigidly in place upon said bottom element.

3. The holding structure of claim 2 wherein the said pin has an external peripheral groove at its central portion adjacent to the inboard terminus of its slotted portion.

4. The holding structure of claim 2 wherein the said pin has an axial bore extending through its slotted portion.

5. The holding structure of claim 2 wherein the upper edge of said sleeve is tapered and the outer edges of the slotted portion of said pin are tapered to facilitate introduction of said slotted portion into the bore of said sleeve.

6. Centering apparatus comprising a bottom element and an upper element, each having a central bore;

a centrally bored element which is centered between said bottom element and said upper element;

a sleeve having longitudinal radial slots, said sleeve being partly engaged in the central bore of said base element;

a pin having radial slots at one end and having its other end engaged in the central bore of said upper element;

said centrally bored element being retained between said bottom element and said upper element with the said sleeve being inserted into the central bore thereof so that the outer surface of the said sleeve is in surface engagement with the said central bore of said centrally bored element;

the said pin being inserted into the said sleeve, whereby the said centrally bored element is restricted between the said upper element and the said bottom element against vertical movement and is restricted by means of said sleeve against horizontal movement.

7. A hub-centering structure for abrasive wheels including:

a bottom element peripherally supporting and defining an abrasive wheel .composition;

a correlative upper element cooperating with said bottom element;

a first bore in the center of said bottom element and a second bore in the center of said upper element;

a sleeve having a first normal diameter extending from a first end thereof to a central portion thereof corresponding with the diameter of said first bore and having a second and larger normal diameter extending from said central portion to the other end thereof, the said central portion comprising a peripheral shoulder on said sleeve;

a plurality of spaced first radial slots in said sleeve extending from said first end longitudinally through said central portion, a plurality of spaced second radial slots extending from said second end longitudinally through said central portion, the said first radial slots alternating with the said second radial slots in the said central portion;

a pin radially slotted at one end and having a normal outer diameter slightly greater than the normal diameter of the bore of said sleeve;

a pin holder comprising a cylinder having a bore in i which the unslotted portion of the said pin is ensaid pin holder being engageable within said second bore of said upper element and having a bottom surface engageable with the said hub over its normally exposed surface;

said pin having its slotted portion engaged within the said sleeve, whereby said sleeve is resiliently engaged over its outer surface with the hub bore and engaged over its inner surface with the said pin to hold the said hub rigid l y in place upon said bnttom 1,501,026 element. 2,135,380

References Cited in the file of this patent UNITED STATES PATENTS 5 546,977 1,265,793 Larsen May 14, 1918 389,253

8 Guay July 8, 1924 Benge Nov. 1, 1938 FOREIGN PATENTS Germany Mar. 18, 1932 Great Britain Mar. 16, 1933 

6. CENTERING APPARATUS COMPRISING A BOTTOM ELEMENT AND AN UPPER ELEMENT, EACH HAVING A CENTRAL BORE; A CENTRALLY BORED ELEMENT WHICH IS CENTERED BETWEEN SAID BOTTOM ELEMENT AND SAID UPPER ELEMENT; A SLEEVE HAVING LONGITUDINAL RADIAL SLOTS, SAID SLEEVE BEING PARTLY ENGAGED IN THE CENTRAL BORE OF SAID BASE ELEMENT; A PIN HAVING RADIAL SLOTS AT ONE END AND HAVING ITS OTHER END ENGAGED IN THE CENTRAL BORE OF SAID UPPER ELEMENT; SAID CENTRALLY BORED ELEMENT BEING RETAINED BETWEEN SAID BOTTOM ELEMENT AND SAID UPPER ELEMENT WITH THE SAID SLEEVE BEING INSERTED INTO THE CENTRAL BORE THEREOF SO THAT THE OUTER SURFACE OF THE SAID SLEEVE IS IN SURFACE ENGAGEMENT WITH THE SAID CENTRAL BORE OF SAID CENTRALLY BORED ELEMENT; THE SAID PIN BEING INSERTED INTO THE SAID SLEEVE, WHEREBY THE SAID CENTRALLY BORED ELEMENT IS RESTRICTED BETWEEN THE SAID UPPER ELEMENT AND THE SAID BOTTOM ELEMENT AGAINST VERTICAL MOVEMENT AND IS RESTRICTED BY MEANS OF SAID SLEEVE AGAINST HORIZONTAL MOVEMENT. 